Jan 23, 2018 | By Julia

As our technology gets smarter, it also gets smaller. Lately, this trend can be seen across a whole range of systems, from smart cars to cellphones to desktop 3D printers. But what of the entire data-sharing system itself? A group of researchers at Northwestern University have begun to investigate this topic precisely, as seen in a new study published in the academic journal Scientific Reports. Their first conclusions have been nothing short of astonishing.

The paper, titled “Inverse-designed broadband all-dielectric electromagnetic devices”, paints a portrait of a world where eyeglasses are impossibly thin, and a smartphone camera is so tiny that it’s invisible to the naked eye. In this world, sensors are highly aerodynamic, and able to conform to the exact angle and slope of an airplane wing. Materials can even act as invisibility cloaks, coating tanks to make them seemingly disappear. While it all may sound like the stuff of science fiction, this world may arrive sooner than we think.

In their study, the Northwestern team documents their breakthrough work in creating highly efficient, non-resonant, broadband metadevices that operate at millimeter-wave frequencies. The innovations achieved here could one day prove revolutionary for defense, consumer products, and telecommunications, including next-gen 5G wireless networks for instance.

comparison between the performance of the inverse-designed device (A to C) and a blazed grating (D to F)

“I feel like we're really on the verge of something big," says Koray Aydin, assistant professor of electrical engineering and computer science at the McCormick School of Engineering. Together with a team of colleagues and graduate students, Aydin is leading the research efforts in inverse-designed metadevices. "There's a lot that needs to be done in the research part, but we're going in the right direction," he says.

Though these broadband metadevices are high-tech, the Northwestern team’s process proved to be surprisingly straightforward. The bulk of the innovating was done using a basic 3D printer purchased from Amazon and inverse design principles. Whereas forward design allows a system to accept input intended for a later version of itself, inverse design starts with a function and asks what structure is needed to achieve the desired result. In this case, that meant using computer modeling, optimization software, and complex algorithms to construct metadevices that could bend or re-focus millimeter waves, while avoiding commonly seen issues of low efficiency, device bulkiness, or narrow bandwidth.

"What we've achieved here is a new way of creating electromagnetic devices that achieve certain functions that conventionally seemed impossible to do," explains Prem Kumar, professor of electrical engineering and computer science in McCormick and of physics and astronomy in the Weinberg College of Arts and Sciences. Somewhat akin to machine learning, the process can lead to unexpected outcomes, Kumar says. Here, that unexpected result was the triumph of functionality over a broad bandwidth.

schematics for the inverse electromagnetic approach for designing free-space metadevices

Francois Callewaert, a graduate student from the McCormick School of Engineering, is credited as the mind behind the inverse design algorithm. His colleague from the physics and astronomy department, Vesselin Velev, assisted with the detailed millimeter-wave measurements. Both worked together with Aydin, who emphasizes the instance when Callewaert’s algorithm spun out the design for a complex geometric shape as utterly “eye-opening.”

In Aydin’s own words, “these were not known shapes, not intuitive shapes.” Such complex geometries presented a problem, however: how would the team go about actually constructing them? Aydin recalls the stumbling block perfectly, noting that conventional methods of manufacturing would be too onerous and costly.

The answer eventually proved to be 3D printing, a solution which Aydin deems “the heart of the study.” The team is officially the first to combine 3D printing and inverse design to make fully functional devices. “The important thing to me is the multidisciplinary nature of it,” Kumar agrees. The innovation means that the team could, for example, design a lens in a way that doesn’t look like a lens at all, he says. Another advantage, according to Aydin, is that the process is imminently scalable from the microwave range to the frequency range we can actually see, thanks in large part to the flexibility of 3D printing.

The results are exciting, to say the least. A few years ago, a study like this would have looked very different because such behavior could only be approximated, notes Alan Sahakian, Professor of Electrical Engineering and Computer Science. This time, however, the team essentially input the behavior they desired into a computer, and the computer then optimizes a structure with that exact behavior. The final prototype then comes out the other end of the 3D printer, and voilà. "It is truly a breakthrough in the way you can solve problems in a seamless and convenient way," Sahakian says.



Posted in 3D Printing Application



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